Les propietats width i height inclouen el contingut, el farciment i la vora, però no el marge. Note that padding and border will be inside of the box e.g. .box {width: 350px; border: 10px solid black;} leads to a box rendered in the browser of width: 350px. The content box can't be negative and is floored to 0, making it impossible to use border-box to make the element disappear.